This application is based on Japanese Patent Application No. 9-155556, filed on Jun. 12, 1997, the content of which is cited herein by reference.
The present invention relates to a hibernation control method for a battery drivable information processing apparatus with a hibernation function, and a battery drivable electronic equipment with a hibernation function.
Conventionally, in a compact electronic equipment such as a battery drivable, portable personal computer with a hibernation function, the control microprocessor in the equipment reads charge/discharge control data present in a battery, and executes charge/discharge control based on the read data.
In order to extend the battery-driven time, such equipment has a power saving function to control the power supply of an LCD (liquid crystal display), HDD (hard disk drive), and the like. Furthermore, in order to protect user data, memory data is saved in a nonvolatile storage medium such as a hard disk by forced hibernation at low battery level.
However, in the above-mentioned prior art, when the equipment is to be driven by a battery up to nearly low battery level in a low-load state by the power saving function, e.g., by turning off the motor of the HDD, and the backlight of the LCD, if abrupt load variations such as forced hibernation (a suspend/resume function of suspending operation by storing active data in a hard disk drive (HDD) and resuming data stored in the HDD after power ON) for saving user data, or the like have occurred, low-battery control that detects the battery voltage/current in a battery driving mode cannot catch up with such variations, and the battery is discharged excessively. That is, the power supply voltage is monitored periodically (e.g., at 1- or 2-sec intervals) by a monitoring circuit so as not to cause detection errors, but the load current is being supplied during this interval. In this case, when a circuit such as a CPU, disk drive, or the like, that causes large load variations operates, the voltage drops suddenly. On the other hand, batteries have different discharge characteristics depending on their manufacturers, i.e., the manufacturer which uses a material with high conduction performance of lithium ions of a battery cell and the one which does not use such material, and a low-battery voltage is set at different values in correspondence with the discharge characteristics.
Conventionally, the low-battery voltage must be corrected to a point that hardly causes load variations as a precaution to take for a battery which is ready to use but has poor discharge characteristics. As a result, the driving time of a battery with high discharge characteristics is decreased, and the battery capacity cannot be effectively used, thus shortening the battery-driving time.
The prior art in such case will be explained below with reference to FIGS. 1 and 2.
In the conventional hibernation, when a battery that causes large capacity variations due to load variations is used, when hibernation is executed (HT: hibernation time) after a battery voltage (VBATT) has reached a low battery level (LV1) in a low-load state (e.g., the battery is discharged to about 95% of its capacity), as shown in FIG. 1, since electric power is consumed to drive the HDD, the battery voltage (VBATT) drops below a battery-driving lowest voltage level (LV3) and reaches an overdischarge level. As a consequence, normal hibernation cannot be done, resulting in data destruction, equipment failures, and the like.
In order to prevent the voltage upon completion of hibernation from reaching an overdischarge level, conventionally, the battery voltage level (low battery level) at the beginning of hibernation is shifted to a level (LV0) higher than the above-mentioned level (LV1) (by correcting the low-battery voltage), thus normally executing hibernation even when a battery that causes large capacity variations due to load variations is used.
However, in this case, since the battery voltage level (low battery level) at the beginning (C) of hibernation is shifted toward higher voltages, the battery driving time is shortened by a battery driving time (TSF) corresponding to that level shift, and consequently, the driving time of a battery with high discharge characteristics is decreased considerably, i.e., the battery cannot be effectively used, thus shortening the battery driving time.